1. Field of the Invention
This invention relates to dot pattern matrix printers and more particularly to high resolution slant head ink jet printers with skewing circuitry which operates modularly on character dot pattern information to conform the information to the slant head pattern.
2. Description of the Prior Art
Dot pattern matrix printers and particularly ink jet printers are frequently used for high speed printing. A printed character is defined by a matrix of dots which are selectively printed or omitted. An ink jet printer contains a plurality of controllable print elements, each including an ink jet, and apparatus for selectively allowing ink to reach the paper or other print medium. Known arrangements of ink jet printers are described in the following U.S. Patents which are assigned to the assignee of the present invention: U.S. Pat. Nos. 3,769,624; 3,769,361; 3,786,517; 3,787,884 and 3,928,855.
The physical size of the ink jets and the apparatus for directing ink flow place limits on the closeness of the spacing of print elements and hence the resolution of a printed character. One known technique for increasing printing resolution is to provide two spaced columnar lines of print elements with each line of print elements printing a different set of alternate dot rows.
However, for extremely high quality, fine resolution printing even closer spacing of the print elements is required. The addition of further columnar lines of print elements would permit increased resolution but would undesirably add to the size, mass and complexity of the print head as well as the complexity of the data control circuitry. It has also been proposed to slant the lines of print elements relative to the direction of print head motion. This would effectively increase the print element resolution in the vertical direction but greatly increase the complexity of the control electronics. For example, if each character dot pattern is defined by a 40 by 24 dot matrix, a triangular shift circuit with 40 separate shift registers varying in length from 1 to 40 positions would be required for each character row of characters to be printed. Three would be required for the present invention. This would represent a tremendous amount of logic circuitry to first skew the data to match the print element locations and then handle the data. Furthermore, 40 bytes of data would be required to fill the shift circuit at the beginning of the character line and again to empty the shift circuit at the end of a character line.
The present invention greatly reduces the size and complexity of the data handling circuitry for a slant head dot pattern matrix printer by dividing each character pattern into 8 mutually exclusive dot pattern modules. Each module contains 12 bytes of 10 bits each which are handled sequentially by a much simplified skewing circuit to rearrange the dot pattern information to conform to the positions of corresponding print elements.